Pros and cons of HRV vs Fresh Air Ventilation in a dry heating/cooling climate.

Welcome to HVAC-Talk.com, a non-DIY site and the ultimate Source for HVAC Information & Knowledge Sharing for the industry professional! Here you can join over 150,000 HVAC Professionals & enthusiasts from around the world discussing all things related to HVAC/R. You are currently viewing as a NON-REGISTERED guest which gives you limited access to view discussions

To gain full access to our forums you must register; for a free account. As a registered Guest you will be able to:

Participate in over 40 different forums and search/browse from nearly 3 million posts.

Yes doors open sometimes. Ultra-Aire bring in fresh air when controller calls for fresh air. Dehumidification and recirculation are independent. This home needs 80 cfm of fresh air to get the air change in 4 hours. Two occupants will not get the CO2 above 800 ppm.
Regards TB

Hmm, I guess our house is totally different so it's not a good comparison. Doors and Windows closed 99% of the time, and no dehumidification. Just a dual fuel system, with humidification to 30%.

Now you guys have piqued my curiousity, so I'm going to borrow a CO2 sensor and check the levels in my house before I make any decisions on this.

The idea is to detect occupancy and inadequate fresh air infiltration. We want a fresh air change in 4-5 hours when occupied by single occupant. Medium sized homes need 70 cfm of fresh air for the air rate and one occupant produces CO2 at a rate that raises 450 ppm CO2 air to 650 ppm. So if the CO2 goes +650 ppm, run the ventilation. When the CO2 goes below 600 ppm, natural ventilation increased or the occupant left the house.
That is the idea. It's about detecting occupancy and a lack of natural .2 ach fresh air change, not excessive CO2 levels. Occupants can handle +2,500 ppm. Hope this helps. Monitoring CO2 will help you understand. CO2meters.com is source of reliable meters.
Regards TB

The idea is to detect occupancy and inadequate fresh air infiltration. We want a fresh air change in 4-5 hours when occupied by single occupant. Medium sized homes need 70 cfm of fresh air for the air rate and one occupant produces CO2 at a rate that raises 450 ppm CO2 air to 650 ppm. So if the CO2 goes +650 ppm, run the ventilation. When the CO2 goes below 600 ppm, natural ventilation increased or the occupant left the house.
That is the idea. It's about detecting occupancy and a lack of natural .2 ach fresh air change, not excessive CO2 levels. Occupants can handle +2,500 ppm. Hope this helps. Monitoring CO2 will help you understand. CO2meters.com is source of reliable meters.
Regards TB

Yes, that's what I was thinking. Is it safe to assume that if my CO2 is below 650 that I'm probably getting the needed ACH I need through infiltration alone?

Yes, that's what I was thinking. Is it safe to assume that if my CO2 is below 650 that I'm probably getting the needed ACH I need through infiltration alone?

One occupant will raise 70 cfm of air from 450 ppm to 650 ppm. Two occupants would raise 70 cfm from 450 ppm to 850 ppm. Yes one person in a home with mixed air that is below 650 ppm would be getting +70 cfm of 450 ppm CO2 outside air. If there was a 100 ppm rise, you would be getting 140 cfm of fresh air.
Regards TB

And what exactly are we "saving" in a residential application by controlling air quality with CO2 detection?

From everything I've read here and elsewhere, I'd say there would be some energy savings by not over-ventilating. I seems to me that it you just ventilate to ASHRAE standards without taking infiltration into consideration, you'll almost always be over ventilating.

And what exactly are we "saving" in a residential application by controlling air quality with CO2 detection?

A moderate climate like Chicago, estimates are $300-$400 for year around conditioning cost of outside air ventilation. Depends on fuels and your idea of temp/%RH levels/air change rates. Half the time outside air needs nothing. Half the time you are not in your home. Half the time, the wind blows hard enough to not need mechanical ventilation.
My wild guess is that CO2 control may save $200 per year in a typical home verses continuous ventilation with without heat recovery. The more air tight the home is, the less you save. Also consider that balance flow ventilation over-ventilates +50% with wind and stack effect forces when compared to make-up or exhaust ventilation.
If we provide fresh air only when occupied and low wind/stack effect, simple make-up without erv is most economical. Also all of the other exhaust devices have make-up air to function.
The bigger deal is that most do not have any ventilation or supplemental humidity control. People with Cadilacs have both. Its not a big deal.
Regards TB

So the answer is, uncontrolled ventilation is out (has been for about 20 years now) in new construction. HRV or ERV is the answer and in a tight house, controlling ventilation with a CO control device has a long ROI. Not saying it is wrong, just a little over the top for home with two people.

So the answer is, uncontrolled ventilation is out (has been for about 20 years now) in new construction. HRV or ERV is the answer and in a tight house, controlling ventilation with a CO control device has a long ROI. Not saying it is wrong, just a little over the top for home with two people.

CO2 control at 2-4 hundred up would be OK. Its the same story for an ERV. I like the concept of an air change in 4-5 hours when needed.
Regards TB

I got the CO2 meter (Supco IAQ50) yesterday evening. I just put it in the living room to start. First results showed about 850PPM, then rising to about 980 before bedtime, then down to 820 in the morning. I also noticed that after we got up and all went into the living room and kitchen, it started to rise again as was about 880 when I left for work. My wife is going to get some more readings during the day.

My first thoughts are
1) This level of CO2 indicates that ventilation would be a good idea in our house.
2) A sensor that switches at 800PPM might work OK in the living room.

I also need to get a vacant period this weekend so I can see if it drops to about 400PPM when we're out.

I got the CO2 meter (Supco IAQ50) yesterday evening. I just put it in the living room to start. First results showed about 850PPM, then rising to about 980 before bedtime, then down to 820 in the morning. I also noticed that after we got up and all went into the living room and kitchen, it started to rise again as was about 880 when I left for work. My wife is going to get some more readings during the day.

My first thoughts are
1) This level of CO2 indicates that ventilation would be a good idea in our house.
2) A sensor that switches at 800PPM might work OK in the living room.

I also need to get a vacant period this weekend so I can see if it drops to about 400PPM when we're out.

Give this some time to go through the weather cycles paticularly wind in varing degrees, calm to 20 mph with occupancy. Your location in the home, the meter location, and air mixing on the home are the issues.
Usually, ventilation when +650 PPM CO2 is adequate to assure fresh air when occupied and low infiltration.
keep us posted
Teddy Bear.